This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Pompe disease is a rare autosomal recessive metabolic muscle disease caused by the deficiency of acid Q glucosidase-GAA, an enzyme that degrades lysosomal glycogen. Pompe disease is characterized by organelle bound, lysosomal, and extra-lysosomal accumulation of glycogen in many body tissues, ultimately leading to multisystemic pathology. There is a broad spectrum of disease ranging from a rapidly progressive form- infantile-onset, to a slow, progressive form-late-onset. All presentations of Pompe disease share a common underlying pathology;i.e., deficiency of GAA with accumulation of glycogen. The late-onset form of Pompe disease progresses less rapidly than the infantile-onset form. Patients present with progressive myopathy of the proximal muscles in the pelvic and shoulder girdles, and a progression of respiratory involvement;is less predictable than the infantile form, with some patients experiencing a rapid deterioration in skeletal and respiratory muscle function leading to loss of ambulation and respiratory failure, others progressing less rapidly, and others with dissociation in the progression of skeletal/respiratory muscle involvement. These patients develop minimal or no cardiomyopathy. Most patients become wheelchair-bound, require ventilator support and ultimately succumb to respiratory failure. This is a multicenter, multinational, open-label extension study of the safety and efficacy of Myozyme treatment in patients with late-onset Pompe disease. Eligible patients will receive an intravenous-IV infusion of 20 mg/kg of Myozyme every other week-qow for a minimum of 52 weeks. Safety and efficacy assessments will be performed at scheduled visits throughout the study treatment period. Adverse events-AE, concomitant medications/therapies and ventilator use will be monitored throughout the study.